1. Field of the Invention
The present invention relates to an oxidative top electrode deposition process, and associated microelectronic device structure.
2. Description of the Related Art
Ferroelectric and high ε thin film capacitors are becoming increasingly important in microelectronics applications, as for example in capacitor structures for advanced memories, in decoupling capacitors and in infrared detectors. In such applications, the ferroelectric or high ε film is typically formed of an oxide perovskite or layered structure perovskite, such as lead zirconium titanate (PbZrTiO3), barium and/or strontium titanates ((Ba,Sr)TiO3), and strontium bismuth tantalates (SrBi2Ta2O9), although other similar materials may also be usefully employed.
Properties of ferroelectric and high ε thin film capacitors depend, in general, on the stoichiometry (atomic relative concentrations of constituent elements) of the film material. While the most common concerns involving the film material relate to cation stoichiometry, the stoichiometric presence of oxygen is likewise important, since the electrical properties of the film are extremely sensitive to oxygen concentration as well.
Formation of capacitor structures utilizing ferroelectric or high ε film oxide materials typically involves vacuum deposition of a metal electrode on top of the oxide layer. The conditions conventionally utilized for deposition formation of such top electrode (TE) structures cause oxygen loss in the underlying ferroelectric or high ε film, particularly at its surface.
Such oxygen loss may be due to chemical and/or physical aspects of the TE deposition process.
Chemical aspects include a higher affinity for oxygen by the TE material as compared to the ferroelectric material, or by other chemical driving forces for deoxygenation, such as the environment in a metal chemical vapor deposition (CVD) process that may be used to deposit the TE.
Physical effects include thermal desorption that may be stimulated by the transfer of energy of an incident atom, such as by sputtering, in instances where sputtering is used as the metallization technique to form the electrode element. Under such conditions, an adatom with superthermal energy (>1 eV) can directly cause ejection of an oxygen atom from the underlying ferroelectric or high e film material.
For dc magnetron sputtering of Ir (for example), adatom energies at the film surface can be on the order of 120 eV for Ar (S. M Rossnagel, C. Nichols, S. Hamaguchi, D. Ruzic, R. Turkot, J. Vac. Sci. and Tech., 14(3) (1996) 1819–1827), and 25 eV for Ir. Since 200 eV Ar is known to modify the surface of crystalline Si to a depth of 28 Å (J. L. Vossen, W. Kern, Eds., Thin Film Processes II, Academic Press, Boston, Mass., 1991, pp. 763), Ar bombardment in a magnetron deposition process may have potentially significant deoxygenation effects on the surface of a ferroelectric such as lead zirconium titanate (PbZrTiO3).
While oxygen loss from the underlying ferroelectric or high ε film material may in principle be compensated by post-annealing the film under oxidizing conditions, such approach depends on the ability of the TE to allow oxygen to diffuse from the annealing atmosphere to the ferroelectric or high ε film surface. An electrode formed of platinum will allow diffusion therethrough of oxygen for that purpose, but other, more desirable TE materials such as Ir and IrO2 will not—they are good oxygen diffusion barriers. Accordingly, for the more desirable TE materials of construction, oxidative post-deposition annealing is not a feasible option.
Accordingly, it would be a significant advance in the art, and is accordingly an object of the present invention, to provide a methodology for forming a top electrode structure, on a ferroelectric or high ε material that is latently susceptible to deoxygenation during the electrode formation step, which effectively prevents the ferroelectric or high ε film from becoming oxygen-deficient during top electrode deposition.
It is another object of the invention to provide a microelectronic device structure including a ferroelectric or high ε film material overlaid with a top electrode structure, wherein the ferroelectric or high e film material is stoichiometrically non-deficient—i.e., is stoichiometrically satisfied—in oxygen content, even at the surface region of the ferroelectric or high ε film material adjacent to the TE layer.
Other objects and advantages of the invention will be more fully apparent from the ensuing disclosure and appended claims.